I completely agree with Kate. You two don’t sound like you are really good friends and it sounds like she does not really care about you or your problems. Real friends would recognize it if you were talking about your issues, even if you talk about them with a smile (talking out of experience, I do the same thing hahah). I would take a minute and think about whether you want to continue this friendship with her or if it is worth saving. Or, as kate said, reach out and see what happens.
I’m not really sure but I was in a similar situation once. I would try to ask your mom why she wants to talk about these topics and if she mentions any issues that she’s struggling with, try to calmly tell her that you are not the person she should talk to about this. This is what worked for me but I obviously don’t know much about your mom or your relationship with her. Maybe you can also tell her that you want to enjoy the limited time you have with her rather than talking about such heavy topics?